What level will Eevee evolve into umbreon?

lvl.21

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That is incorrect. Eevees do not evolve at a certain level. As a matter of fact, they don't evolve at all, on their own. They must: be given a stone, (Vaporeon, Jolteon, and Flareon,) be leveled up during a certain time of the day, with high happiness, (Espeon evolves during the day, while Umbreon evolves at night,) or be leveled up near a certain rock, (Leafeon needs to be leveled up near a Moss Rock, while Glaceon needs to be leveled up near an Ice Rock.)

Be aware that certain Eeveelutions may not be available in certain games. If you're in the Kanto region, you'll only have access to Vaporeon, Jolteon and Flareon. If you're in the Johto region, you'll have access to those three, plus Espeon and Umbreon. And if you're in the Sinnoh region, you'll have all access to all seven Eeveelutions.